AU2017203320B2 - Compression method and apparatus for an apparatus for capturing co2 by low-temperature separation - Google Patents

Compression method and apparatus for an apparatus for capturing co2 by low-temperature separation Download PDF

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AU2017203320B2
AU2017203320B2 AU2017203320A AU2017203320A AU2017203320B2 AU 2017203320 B2 AU2017203320 B2 AU 2017203320B2 AU 2017203320 A AU2017203320 A AU 2017203320A AU 2017203320 A AU2017203320 A AU 2017203320A AU 2017203320 B2 AU2017203320 B2 AU 2017203320B2
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gas
separated
compressor
fan
flow rate
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Cyril Defaye
Ludovic Granados
Mathieu LECLERC
Frederick Lockwood
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LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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Air Liquide SA
LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/063—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream
    • F25J3/067—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the separated product stream separation of carbon dioxide
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
    • B01D3/14—Fractional distillation or use of a fractionation or rectification column
    • B01D3/143—Fractional distillation or use of a fractionation or rectification column by two or more of a fractionation, separation or rectification step
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/002—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols by condensation
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0204—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the feed stream
    • F25J3/0223—H2/CO mixtures, i.e. synthesis gas; Water gas or shifted synthesis gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0228—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream
    • F25J3/0266—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream characterised by the separated product stream separation of carbon dioxide
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
    • F25J3/0295—Start-up or control of the process; Details of the apparatus used, e.g. sieve plates, packings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0605—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation characterised by the feed stream
    • F25J3/0625—H2/CO mixtures, i.e. synthesis gas; Water gas or shifted synthesis gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
    • F25J3/06—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by partial condensation
    • F25J3/0695—Start-up or control of the process; Details of the apparatus used
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2210/00—Processes characterised by the type or other details of the feed stream
    • F25J2210/70—Flue or combustion exhaust gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/02—Compressor intake arrangement, e.g. filtering or cooling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2230/00—Processes or apparatus involving steps for increasing the pressure of gaseous process streams
    • F25J2230/30—Compression of the feed stream
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2260/00—Coupling of processes or apparatus to other units; Integrated schemes
    • F25J2260/60—Integration in an installation using hydrocarbons, e.g. for fuel purposes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/02—Internal refrigeration with liquid vaporising loop
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2270/00—Refrigeration techniques used
    • F25J2270/80—Quasi-closed internal or closed external carbon dioxide refrigeration cycle
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
    • F25J2280/00—Control of the process or apparatus
    • F25J2280/02—Control in general, load changes, different modes ("runs"), measurements
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/40—Capture or disposal of greenhouse gases of CO2

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Separation By Low-Temperature Treatments (AREA)
  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

Method for compressing a gas that is to be separated in a low-temperature C02 separation unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, the gas that is to be separated is compressed in a compressor to produce a compressed gas, wherein the inlet pressure of the gas that is to be separated, entering the compressor, is modified according to the C02 content and/or the flow rate of the gas that is to be separated so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor. 1/1 o> Fge CCY) Figure 1

Description

1/1
o>
CCY)
Fge
Figure 1
COMPRESSION METHOD AND APPARATUS FOR AN APPARATUS FOR CAPTURING C02 BY LOW-TEMPERATURE SEPARATION
This application claims priority from French patent application number 1654808 filed on 27 May 2016, the contents of which are to be taken as incorporated herein by this reference. The present invention relates to a method and an apparatus for an apparatus for capturing C02 by low-temperature separation. The gases to be separated in order to capture the C02 that they contain are often gases the composition and flow rate of o which may vary. The increase in the concentration of carbon dioxide in the atmosphere is largely responsible for global warming. C02 of human origin is essentially emitted into the atmosphere through the burning of fossil fuels in power stations and in a certain number of industrial units such as cement works, hydrogen production units or even steelworks. In the context of reducing the emissions of greenhouse gases and/or the production of C02 used for enhanced oil recovery, a unit that captures and purifies C02 by cryogenic means can be used downstream of the C0 2-emitting plants. The cryogenic capture and purification of C02 are essentially based on the partial o condensation of the C02 at temperatures close to its triple point, which may be supplemented by one or more distillations to increase the C02 purity of the end product. In order to perform these partial condensations and distillation, it is going to be necessary to compress the gases that are to be purified, to dry them and then to cool them in order to form a C0 2-enriched liquid phase and a gaseous phase enriched in incondensable gases that will be separated in one or more partial condensation pots. With this kind of method, capture efficiencies of between 80 and 95% are achievable. The liquid C02 obtained is usually separated into at least two streams. The first stream is vaporized directly against the gas that is to be purified to supply the frigories at the highest temperatures. The second stream is expanded before being vaporized so as to supply the frigories necessary for cooling the gas that is to be purified to the lowest temperatures of the cryogenic part, namely to temperatures close to the triple point of C02. These (at least) two vaporized streams are then
1a
compressed in a COC02 compressor the streams at the lowest pressures being injected into the compressor further upstream than the other streams ofC02. The principles of partial condensation and of distillation are based on the partial pressure of each constituent of the gas. In the context of C02 capture and purification, the partial pressure of C02 at the inlet to the cryogenic part of the method is thus a key parameter in the sizing of the separation equipment. For example, the lower the partial pressure of C02: • the more the gas will need to be cooled in order to begin to condense it, which means to say in order to begin to form the C0 2-enriched liquid phase * as a result, the distribution of the liquid C02 between the low-pressure streams and those not being expanded will need to be adjusted: the flow rates of expanded liquid C02 will be increased in order to supply more low-temperature frigories o 0 for the same ultimate cooled temperature, the lower the C02 recovery efficiency will be and vice versa. If the composition of the gas that is to be purified changes, the partial pressure of C02 will change. That modifies the exchanges of heat needed and thus the distribution of the "low" and "medium" pressure streams of C02 that are needed to supply the correct amounts of cold at the various temperatures. Hence, the sizing of the C02 compressor will therefore need to take into account the fact that the distribution between the lower-pressure fluids and the other fluids resulting from the vaporization of the liquid C02 has changed. That will lead to oversizing and mean o that the operation of the compressor is not optimal. For example, if the C02 composition of the gas that is to be purified drops with respect to the nominal C02 composition, the compressor will need to be capable of compressing the low pressure flow rate that is increased over and above its nominal value. The compressor will therefore need to be sized for the operating scenario of the low composition, by increasing its capacity. In nominal operation, when the composition is nominal, the flow rate sent to the compressor will therefore be well within its capacities, so its operation will therefore not be optimal. In addition, it may happen that the liquid streams of C02 are vaporized in exchangers which are distinct from one another according to their pressure and/or temperature following expansion. As a result, the change in distribution between the various fluids which will need to be vaporized will have an impact on the performance of these heat exchangers. According to the same example as before, the exchanger in which the lowest-pressure fluid vaporizes will need to be sized for the low- composition operating scenario and will therefore be oversized for the scenario of operating with the nominal composition. The reverse is true of the other exchanger regarding the other level or levels of vaporization: it will be oversized for operation at low composition. In order to avoid these various oversizings, which will affect the price and performance of the capture unit, the proposed solution is to provide a design of compressor for the gas that is to be purified that allows a variation in outlet pressure. This pressure will then be controlled according to the C02 composition of the gas that is to be purified in order to achieve substantially the same C02 partial pressure at the o inlet to the cryogenic part whatever the composition of the gas that is to be purified. All the on-costs and losses of efficiency of the cryogenic part and of the C02 compressor are therefore avoided, and these will be easier to control because substantially the same phenomena will occur within the cryogenic part whatever the quality of the gas that is to be treated. In most cases, a variation in the C02 composition of the gas that is to be purified is accompanied by a change to the flow rate of the gas that is to be purified. The change in compressor outlet pressure of the gas that is to be purified as a function of the C02 composition will also make it possible to adjust the volumetric flow rate entering the cryogenic part. By contrast, the inlet to this compressor will be o affected by the changes in volumetric flow rate. It is possible to conceive of oversizing this compressor, but the costs and performance of the unit would be modified as a result especially given that this compressor represents the greatest proportion of the capture and purification costs. In instances in which the compression of the gas that is to be purified begins in a fan, the solution proposed involves oversizing this fan, which will have a marginal impact on the total cost, and controlling its outlet pressure (oversizing a fan is less expensive than oversizing a main compressor). The outlet pressure of this fan will therefore be adjusted so as to achieve a volumetric flow rate that remains substantially the same whatever the quality of the gas that is to be purified. Thus, the sizing of the main compressor of the unit will be unaffected and it will be more easy to control because its inlet volumetric flow rate will remain constant: control over the pressure at the outlet of the main compressor will not be impacted by undesired variations in its inlet volumetric flow rate. For problems with the control and sizing of the fan, a second fan may also be used in parallel so as not to oversize the main fan. As a result, an output pressure higher than its nominal pressure may be demanded of the main fan without it also having to cope with an additional flow rate compared to its nominal flow rate. According to one subject of the invention, there is provided a method for compressing a gas that is to be separated in a low-temperature C02 separation unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, the gas that is to be separated is compressed in a compressor to produce a compressed gas, characterized in that the inlet pressure of the gas that is to be separated, entering the compressor, is modified according to the C02 content and/or the flow rate of the gas that is to be separated so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor. According to a further subject of the invention there is provided a method for compressing a gas that is to be separated in a low-temperature C02 separation unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, the gas that is to be separated is compressed in a compressor to produce a compressed gas, wherein the inlet pressure of the gas that is to be separated, entering the compressor, is modified according to the C02 content so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor. According to other optional aspects: - If the C02 content of the gas that is to be separated drops and/or the flow rate of the gas that is to be separated increases, the pressure of the gas that is to be separated, at the inlet to the compressor, is increased. - The volumetric flow rate of the flow of gas that is to be separated entering the compressor is substantially constant. - The gas that is to be separated is pressurized upstream of the compressor by means of at least one fan which produces a variable-pressure flow rate. - At least a proportion of the gas compressed in the fan is sent to the compressor to be compressed. - The composition of the flow compressed in the fan is not modified between the fan and the compressor.
- At least part of the flow compressed in the fan is separated between the fan and the compressor to clean it of NOx and/or of SOx and/or of dust. - The fan is made up of two fan blowers connected in parallel or of a single fan blower. - The fan has a compression ratio of less than 2 and/or has just one single compression impellor. - The gas that is to be separated contains at least 35 dry mol% C02. - The gas that is to be separated contains at least 50 dry mol% C02. - The gas that is to be separated contains at least 80 dry mol% C02. - The gas that is to be separated contains C02 and at least one other gas found in the group comprising methane, oxygen, nitrogen, argon, hydrogen, carbon monoxide. - The gas that is to be separated comes from an oxycombustion unit or a cement works. According to another subject of the invention there is provided a method of separating a gas that is to be separated in a low-temperature C02 separation unit in which the gas that is to be separated is compressed as described hereinabove, cooled in a heat exchanger, separated by at least one partial condensation step and/or at least one distillation step to produce a C02-rich flow and a fluid resulting from the partial condensation and/or distillation heats up in the heat exchanger. For preference, the fluid is a liquid, preferably rich in C02, which vaporizes at at least one pressure in the heat exchanger. According to another aspect of the invention, there is provided an apparatus for compressing a gas that is to be separated in a low-temperature C02 separation unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, comprising a compressor for compressing the gas that is to be separated to produce a compressed gas, characterized in that it comprises means for modifying the inlet pressure of the gas that is to be separated, entering the compressor, according to the C02 content and/or the flow rate of the gas that is to be separated so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor. According to a further subject of the invention there is provided an apparatus for compressing a gas that is to be separated in a low-temperature C02 separation
5a
unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, comprising a compressor for compressing the gas that is to be separated to produce a compressed gas, wherein it comprises means for modifying the inlet pressure of the gas that is to be separated, entering the compressor, according to the C02 content so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor. The said fan could also be the one situated upstream of the C02 capture process in the "conventional" flue-gas treatment sequence of an energy production plant (deNOx and/or deSOx and/or filtration, etc.). This fan (an inducted draft fan or ID fan) is used to draw out the flue gases from the boiler. What is meant here by a "fan" or "fan blower" is a compressor of which the energy expenditure, as a result of the treated gas flow rate and compression ratio, is considerably lower than that of the main compressor of the installation, and for example of the order of 2 to 6% thereof. The compression ratio of such a fan blower is generally lower than 2.
A "C0 2-rich" gas or fluid contains at least 35% C02, or even at least 50% C02 or even at least 80% C02. A volumetric flow rate that is substantially constant varies by less than 5%, or even than 2%. The invention will be described in greater detail with reference to the figure. The gas that is to be separated is generated by an energy generation unit (but could for example come from a cement works), which may for example comprise an oxycombustion unit followed by a series of units for scrubbing the C0 2-rich gas of NOx and/or of SOx and/or of dust. The generation unit 1 produces a gas 3 containing o at least 50 dry mol% carbon dioxide, as well as other gases that may be hydrogen, carbon monoxide, oxygen, nitrogen and argon. Depending on the fuel used for the oxycombustion, the composition and therefore in general the flow rate of this gas 3 may vary. This gas 3 is compressed by a fan 5 having a compression ratio of at most 2 to produce a gas 7 at a pressure slightly above atmospheric pressure. At least a proportion of the gas 7 is compressed by a compressor 9. The other proportion (gas 10) may be recirculated to the generation unit 1 when the fan is used for drawing the flue gases (ID fan). The gas 11 produced by the compressor 9 is cooled in a heat exchanger then sent to a separation unit using partial condensation and/or distillation to produce at least one C0 2-rich fluid. At least one fluid produced by the partial o condensation and/or distillation heats up or even vaporizes in the heat exchanger. If the C02 content of the gas 11 drops at the inlet to the separation unit 13, that means that the C02 in the gas 3 is diluted with incondensable gases and therefore that the flow rate of the gas 11 entering the CPU increases. In that case, the pressure at the outlet of the fan 5 needs to be increased in order to decrease the volumetric flow rate at the inlet to the compressor 9. Likewise, if the C02 content of the gas 11 increases at the inlet to the separation unit 13, that means that the C02 in the gas 3 is less diluted by incondensable gases and therefore that the flow rate of the gas 11 entering the CPU drops. In this case, the pressure at the outlet of the fan 5 needs to be reduced in order to increase the volumetric flow rate at the inlet to the compressor 9. In the example, the pressure at the inlet to the compressor 9 is regulated according to the flow rate 11 measured by the flow meter 8 for the gas 7 and/or of the flow meter 15 for the gas 11 is used. This pressure is varied by modifying the compression ratio of the fan 5. Thus, if the flow rate 7 is 110 000 m 3/h, the pressure at the inlet to the compressor 9 will be 1.17 bar, whereas if the flow rate 7 increases to 136 000m 3/h, the pressure at the inlet to the compressor 9 will be just 1.01 bar. In the former instance, the flow rate 7 will be 127 000 m 3/h and in the latter, 126 500m 3/h. Thus, for a volumetric flow rate 7 that increases by 24%, the volumetric flow rate 7 drops by less than one per cent and therefore remains substantially constant. It will be appreciated that, between the point at which the flow 10 is bled off o and the compressor 9, the gas coming from the fan 5 may be cleaned in different ways, for example to remove NOx and/or SOx. Otherwise, the fan may be a fan 5 all of the compressed gas from which is sent to the compressor 9. In that case, the flow 10 does not exist and the flow 7 is not cleaned between the fan 5 and the compressor 9. The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of o this application. Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

Claims (12)

The claims defining the invention are as follows:
1. Method for compressing a gas that is to be separated in a low temperature C02 separation unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, the gas that is to be separated is compressed in a compressor to produce a compressed gas, wherein the inlet pressure of the gas that is to be separated, entering the compressor, is modified according to the C02 content so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor.
2. Method according to Claim 1, in which if the C02 content of the gas that is to be separated drops and/or the flow rate of the gas that is to be separated increases, the pressure of the gas that is to be separated, at the inlet to the compressor, is increased.
3. Method according to Claim 1 or 2, in which the volumetric flow rate of the flow of gas that is to be separated entering the compressor is substantially constant.
4. Method according to Claim 1, in which the gas that is to be separated is pressurized upstream of the compressor by means of at least one fan which produces a variable-pressure flow rate.
5. Method according to Claim 4, in which the composition of the flow compressed in the fan is not modified between the fan and the compressor.
6. Method according to Claim 4, in which the flow compressed in the fan is separated between the fan and the compressor to clean it of NOx and/or of SOx and/or of dust.
7. Method according to any one of Claims 4 to 6, in which the fan is made up of two fan blowers connected in parallel or of a single fan blower.
8. Method according to any one of Claims 4 to 7, in which the fan has a compression ratio of less than 2.
9. Method according to any one of the preceding claims, in which the gas that is to be separated contains at least 35 dry mol% C02.
10. Method of separating a gas that is to be separated in a low-temperature C02 separation unit in which the gas that is to be separated is compressed according to one of the preceding claims, cooled in a heat exchanger, separated by at least one partial condensation step and/or at least one distillation step to produce a C02-rich flow and a fluid resulting from the partial condensation and/or distillation heats up in the heat exchanger.
11. Method according to Claim 10, in which the fluid is a liquid, preferably rich in C02, which vaporizes in the heat exchanger.
12. Apparatus for compressing a gas that is to be separated in a low temperature C02 separation unit using at least one partial condensation step and/or at least one distillation step, in which the gas that is to be separated has a variable composition and/or variable flow rate, comprising a compressor for compressing the gas that is to be separated to produce a compressed gas, wherein it comprises means for modifying the inlet pressure of the gas that is to be separated, entering the compressor, according to the C02 content so as to reduce the variations in volumetric flow rate of the gas that is to be separated entering the compressor.
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US10746463B2 (en) 2020-08-18
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